The invention relates to a two-for-one twisting spindle having a pneumatically actuated threading device.
In two-for-one twisting spindles, the thread is generally drawn off upwardly from the stationary supply bobbin, introduced into the upper end of a thread inlet tube, deflected downwardly and guided by a thread brake into the spindle rotor or into the spindle shaft, which it leaves again in the radial direction through a thread guide channel.
After leaving the thread guide channel, the thread is guided upwardly and, during the twisting, forms a balloon rotating about the supply bobbin. The thread then runs through a thread guide and is wound, twisted, onto a take-up bobbin.
On modern two-for-one twisting machines, the threading of the thread takes place by means of compressed air and a threading injector. Compressed air is fed to the threading injector for the threading process. The air flowing out of the threading injector produces in the thread guide channel an air flow directed outwardly to the mouth of the thread guide channel. A negative pressure is produced in the part of the spindle shaft configured as a hollow spindle. The sucked-in air draws the already held thread into the mouth at the upper end of the thread inlet tube. The air flow conveys the thread outwardly through the thread guide channel. After leaving the thread guide channel, the thread can be grasped manually by the operator and drawn off from the supply bobbin and positioned for further processing steps.
German Patent Publication DE 3012427 C2 discloses a two-for-one twisting spindle having a pneumatically actuated threading device, in which the spindle rotor has a coaxially extending connection channel, through which compressed air is fed. In the storage disc of the spindle rotor, the thread channel feeding thread from above and the connection channel feeding the compressed air from below in each case open, after a deflection, into the thread guide channel of the storage disc. The compressed air entering the connection channel during the threading process flows through the injector and produces the suction action required to suck in the thread in the hollow spindle in the upper part of the spindle rotor. On ending the threading process, the compressed air feed is interrupted again.
German Patent Publication DE 10250423 A1 shows a two-for-one twisting spindle having a pneumatically actuated threading device, in which the compressed air channel in the lower part of the spindle shaft is firstly guided centrally and, before reaching the thread storage disc, is guided as an oblique bore. Adjoining the compressed air channel in the spindle shaft is an air channel in an injector element which opens as an injector into the thread channel and therein produces the required air flow radially outwardly.
The production costs of these known embodiments are high. In particular, the manufacturing of the channels in the spindle shaft is expensive. The efficiency of the known designs is unsatisfactorily low. A measure of the efficiency in this case is the static or dynamic negative pressure which can be produced in the thread inlet tube or in the thread channel as a function of the pressure of the pressure source used. The lower the pressure of the compressed air source for achieving an adequately high negative pressure for sucking in the thread, the more economically or efficiently the threading process can be carried out. The configuration of the air guide in the known embodiments to the thread channel limits the efficiency.
In addition, the abrupt deflection of the air flow through around 90° or more leads to the fact that the compressed air leaving the compressed air channel firstly impinges perpendicularly on the wall of the injector element before the compressed air flow is deflected and accelerated in the injector element. The swirlings occurring at the deflection point reduce the efficiency of the injector element as the compressed air must be fed at a higher pressure to compensate this effect.